The Harvard Pediatric Health Service Research (HSR) Fellowship Program seeks to train researchers who can fundamentally improve the capacity of the US health care system to meet the needs of children and families, including socioeconomically disadvantaged populations. This mature Program, first funded in 1994 by AHRQ, is now fully integrated across its 3 core sites: Children's Hospital Boston, Mass General Hospital for Children, and the Harvard Dept. of Ambulatory Care and Prevention. In the last 10 years it has graduated a diverse, multi-disciplinary group of 36 trainees drawn from a large, high-quality applicant pool. They have published 290 peer-reviewed papers, many in high-impact journals, and 92% remain in academic positions in leading pediatric centers. Trainees' research has addressed all major AHRQ HSR priority areas. Our Program is built upon a highly structured curriculum (including training in core competencies needed for independent HSR careers); a collaborative; multi-disciplinary cadre of senior mentors and faculty (including methodologists in the basic sciences of HSR) with well funded research portfolios; and high expectations for trainees to meet clear milestones for national presentations, publications, and grant submissions. A dynamic evaluation system has allowed rapid-cycle improvement in all aspects of our Program, including enhanced support for transitions to academic careers. In this renewal application, we highlight new initiatives in frontier areas in child HSR including: use of genetic information in pediatrics; IT innovations in personal health records to promote family centered care; comparative effectiveness research using large integrated databases to inform clinical and policy decisions; approaches to improving population health through collaborations among health care and public health systems, payers, and community partners; quasi-experimental methods for evaluating Ql interventions (including initiatives to reduce disparities); and new methods for detecting and preventing harm. We will continue to build partnerships that allow direct access to hospitals and ambulatory care systems, insure that trainees benefit from other Harvard AHRQ Programs, and leverage our connections with IHI and NICHQ for access to real world work on health care innovation, translation, implementation, and dissemination. These initiatives, along with our already robust HSR portfolio, utilize fully the cross-disciplinary resources at Harvard to train a generation of leaders in child HSR.